A slang term for an inexpensive, small-caliber revolver. Dave Kopel, Research Director at the Independence Institute, explains:

The “Saturday night special” is in part a linguistic descendant of the racist phrase "Niggertown Saturday Night." The obvious implication of the phrase "Saturday night special" is that it is a gun used by "niggers" to shoot each other with during their wild Saturday nights. No one denies that the people disarmed by a "Saturday night special" ban would be predominantly poor and non-white.

Saturday Night Specials are preferred by the lower classes, therefore they must be dangerous.